Toxoplasma gondii encephalitis occurs in up to 30% of HIV-infected individuals with latent infection. Anti-toxoplasma chemotherapy is often toxic, and despite adequate therapy, disease recurs in up to 50% of patients with AIDS. An understanding of the cellular immune response to T. gondii infection may aid in the development of improved predictors of the risk for recrudescent disease, and may lead to effective immunotherapies. We have constructed recombinant vaccinia viruses that express the 28-kD toxoplasma antigen. A second vector that expresses the p22 antigen of T. gondii is currently being constructed in our laboratory. By using these vectors to induce autologous EBV-transformed lymphoblasts to express toxoplasma antigens, we can examine cytotoxic T-cell activity of cells derived from individuals with a history of T. gondii infection. We propose to study toxoplasma-specific CTL responses of T. gondii-seropositive, HIV- infected individuals.